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History

Kirk McKusick 9ab73fd11a Within ufs, the ffs_sync and ffs_fsync functions did not always check for and/or report I/O errors. The result is that a VFS_SYNC or VOP_FSYNC called with MNT_WAIT could loop infinitely on ufs in the presence of a hard error writing a disk sector or in a filesystem full condition. This patch ensures that I/O errors will always be checked and returned. This patch also ensures that every call to VFS_SYNC or VOP_FSYNC with MNT_WAIT set checks for and takes appropriate action when an error is returned. Sponsored by: DARPA & NAI Labs.		2002-10-25 00:20:37 +00:00
..
ffs_alloc.c	intmax_t is printed with %jd, not %lld.	2002-09-19 03:55:30 +00:00
ffs_balloc.c	This update is a performance improvement when allocating blocks on	2002-10-22 01:14:25 +00:00
ffs_extern.h	Introduce typedefs for the member functions of struct vfsops and employ	2002-08-13 10:05:50 +00:00
ffs_inode.c	- Convert locks to use standard macros.	2002-09-25 02:49:48 +00:00
ffs_snapshot.c	Within ufs, the ffs_sync and ffs_fsync functions did not always	2002-10-25 00:20:37 +00:00
ffs_softdep_stub.c	Add a missing argument to the stub for softdep_setup_freeblocks.	2002-07-20 04:07:15 +00:00
ffs_softdep.c	We must be careful to avoid recursive copy-on-write faults when	2002-10-23 21:47:02 +00:00
ffs_subr.c	I forgot this bit of uglyness in the fsck_ffs cleanup.	2002-07-31 07:01:18 +00:00
ffs_tables.c	This commit adds basic support for the UFS2 filesystem. The UFS2	2002-06-21 06:18:05 +00:00
ffs_vfsops.c	Within ufs, the ffs_sync and ffs_fsync functions did not always	2002-10-25 00:20:37 +00:00
ffs_vnops.c	Fix a file-rewrite performance case for UFS[2]. When rewriting portions	2002-10-18 22:52:41 +00:00
fs.h	Define two new superblock file system flags:	2002-10-14 17:07:11 +00:00
README.snapshot	Fix a type: s/your are/you are/	2002-07-12 19:56:31 +00:00
README.softupdates
softdep.h	Add support to UFS2 to provide storage for extended attributes.	2002-07-19 07:29:39 +00:00

README.softupdates

$FreeBSD$

Using Soft Updates

To enable the soft updates feature in your kernel, add option
SOFTUPDATES to your kernel configuration.

Once you are running a kernel with soft update support, you need to enable
it for whichever filesystems you wish to run with the soft update policy.
This is done with the -n option to tunefs(8) on the UNMOUNTED filesystems,
e.g. from single-user mode you'd do something like:

	tunefs -n enable /usr

To permanently enable soft updates on the /usr filesystem (or at least
until a corresponding ``tunefs -n disable'' is done).


Soft Updates Copyright Restrictions

As of June 2000 the restrictive copyright has been removed and 
replaced with a `Berkeley-style' copyright. The files implementing
soft updates now reside in the sys/ufs/ffs directory and are
compiled into the generic kernel by default.


Soft Updates Status

The soft updates code has been running in production on many
systems for the past two years generally quite successfully.
The two current sets of shortcomings are:

1) On filesystems that are chronically full, the two minute lag
   from the time a file is deleted until its free space shows up
   will result in premature filesystem full failures. This
   failure mode is most evident in small filesystems such as
   the root. For this reason, use of soft updates is not
   recommended on the root filesystem.

2) If your system routines runs parallel processes each of which
   remove many files, the kernel memory rate limiting code may
   not be able to slow removal operations to a level sustainable
   by the disk subsystem. The result is that the kernel runs out
   of memory and hangs.

Both of these problems are being addressed, but have not yet
been resolved. There are no other known problems at this time.


How Soft Updates Work

For more general information on soft updates, please see:
	http://www.mckusick.com/softdep/
	http://www.ece.cmu.edu/~ganger/papers/CSE-TR-254-95/

--
Marshall Kirk McKusick <mckusick@mckusick.com>
July 2000